"Power MOSFETs are generally designed as switches. Total power dissipated is the sum of "on"-state losses plus losses generated during the very short switching intervals. Desirable characteristics include the lowest possible ON resistance, high breakdown voltage, very high gain (g or Gm ), minimum switching losses, and a low gate threshold voltage VGS(th)

In those applications requiring operation in the linear region, these characteristics are not ideal. Firstly, Gm is too high and, secondly VGS(th)has a negative temperature coefficient which makes it impossible to maintain constant drain current without negative feedback. Finally, and most dangerous of all, large switchmode MOSFETs exhibit a phenomenon known as "hot spotting" or current tunnelling."

Thanks for the reference. I'll read it in detail. My initial impression is that these guys are power jocks and know little about audio amplifiers. Their comment that MOSFETs have more gm than desirable for linear applications is patently stupid.

The 10 ms safe area line on this transistor is at 2500 watts - very impressive. This would appear to be 8 times the 300-watt rating for the IRFP 240. But I don't know anything else about this transistor, for example, how big is the die, how big are the capacitances, how much does it cost, does it have a p-channel complement?